The objective of this research is to determine the cellular requirements for activation of antibody-producing (B) cells by thymus T dependent (TD) and T independent (TI) antigens by determining 1) the types of cells which are activated by TI antigens, in particular, whether TI antigens can activate memory B cells, suppressor T cells, or helper or amplifier T cells, and 2) whether T cells are required for the induction of IgG memory responses by TD antigens. Antibody responses will be measured by the Jerne plaque assay and by passive hemagglutination. The effects of priming with TI antigens will be measured by transferring the cell type to be tested with appropriate cells from mice primed with TD antigens to irradiated recipient mice. The role of T cells in induction of IgG memory responses will be measured by transferring primed B cells from athymic nude mice to irradiated recipients together with syngeneic primed T cells.